1. Field of the Invention (Technical Field)
The present invention relates to electrochemical detection of analytes using thick-film electrodes, including screen-printed thick-film electrodes, in microfluidic devices, including separation devices such as capillary electrophoresis microsystems.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Microscale separation devices, particularly chip-based, micromachined capillary electrophoresis (CE) systems, have witnessed an explosive growth in recent years. These miniaturized devices present the ability to shrink conventional “bench-top” separation systems while providing major advantages in speed, cost, portability, and solvent/sample consumption. As the field of chip-based separation microsystems continues its rapid growth, there is an urgent need for developing compatible detection modes and systems. Much of the work on CE microchips uses laser-fluorescence detection. Yet, such detection requires a large and expensive supporting optical system, and is limited to analytes that fluoresce or are amenable to derivatization with a fluorophore. Microscale CE systems are described generally in, among others, U.S. Pat. Nos. 5,904,824, 6,068,752 and 6,103,199.
Electrochemical detection is used in a wide variety of areas. Such detection offers remarkable sensitivity (comparable to that of fluorescence), tunable selectivity, and low-volume requirements. Electrochemical detection is generally described In J. Wang, Analytical Electrochemistry, 2nd Ed., Wiley-VHC, New York, 2000. Electrochemical detection has proven to be extremely useful for conventional CE systems based on fused-silica capillaries, but has rarely been used for planar micromachined CE chips. The major challenges for such integration are similar to those of conventional CE systems, namely isolation of the working electrode from the high separation voltage and its proper alignment with the capillary. The use of integral lithographically-fabricated thin-film electrodes and separation channels, with the thin-film electrode located inside the exit of the channel, have been described (U.S. Pat. Nos. 6,045,676 and 5,906,723); Gavin and Ewing (Anal. Chem. 1997, 69, 3838) developed a thin-film microfabricated electrochemical array detector for planar CE chips, while certain of the inventors herein have described an on-chip thin-film detector based on sputtering the working electrode directly onto the channel outlet (Anal. Chem. 1999, 71, 3901).
Microscale fluidic devices coupled with electrochemical detection means are applicable to a wide variety of environmental, research, industrial and medical applications, among others. For example, such devices could be used in operating rooms, emergency departments, intensive care units, ambulances, clinics and the like for rapidly and reliably monitoring a wide range of analytes. While CE is the primary electrically driven separation modality used in microfluidic applications, other separation modalities have been described for microscale fluidic devices, including pump and other mechanical transport devices.